Lithium-ion secondary cells or batteries are commonly used as power sources in portable electronic devices. Such rechargeable cells generally use a lithium transition metal oxide (e.g., lithium colbaltate) positive electrode and a negative electrode composed of a highly porous carbonaceous material, typically graphite. The carbonaceous material, however, may also include other carbons, metal and/or a pyrolyzed organic material. A lithium-ion soluble electrolyte is provided between the two electrodes, and the cell is charged. During the electrochemical process of charging, some of the lithium ions in the positive electrode migrate from the positive electrode (serving as the anode) and intercalate into the negative electrode (serving as the cathode). The ability of an electrode to accept ions for intercalation depends largely, for example, on the crystallinity, the microstructure, the porosity, and/or the micromorphology of the material comprised by the electrode. During discharge, the negative charge held by the negative electrode (now serving as the anode) is conducted out of the battery through its negative terminal and the lithium ions migrate through the electrolyte and back to the positive electrode (now serving as the cathode). While it is understood that the terms “anode” and “cathode” apply to each of the negative and positive electrodes depending upon whether the cell is being charged or is discharging, hereinafter the term “anode” is used to refer to the negative electrode, and the term “cathode” is used to refer to the positive electrode.
During the first electrochemical intercalation of lithium ions into the carbonaceous anode material, some lithium is irreversibly consumed and a significant amount of capacity cannot be recovered in the following discharge. This irreversible capacity loss, which mainly depends on the type of carbonaceous anode material and electrolyte solution used, is explained on the basis of the reduction of the electrolyte solution and the formation of a passivating film at the LixC interface. Chemical combination of lithium to the active surface functional groups of carbon may also play an important role in this irreversible capacity loss. Another source of irreversible capacity is the reduction of Li ion concentration due to the ions' strong binding with anode material followed by the growth of dendritic forms of Li. This irreversible capacity loss affects the cell balancing and lowers the energy density of lithium-ion batteries.
At present, special-types of “hard carbon” or graphite are used as anode materials in commercial lithium-ion batteries. The carbon/graphite materials deliver a reversible specific capacity of only ˜370 mAh/g, corresponding to the chemical formula of LiC6, as compared to 3830 mAh/g for metallic lithium. The main advantage of these special carbon materials is their relatively low irreversible capacity loss (≤10%) combined with their high storage capacity (>400 mAh/g). However, the methods of synthesizing these special carbon materials do not allow independent fine tuning or control of pore size distribution, crystallinity and surface area of the materials, which could further improve capacity and reduce irreversible capacity loss.
Based on the foregoing, there is a need in the art to synthesize inexpensive carbon-based electrode materials that have increased reversible capacity and decreased irreversible capacity loss for use in lithium-ion battery systems. It would be further advantageous if the materials could be synthesized using methods that could control pore size distribution, surface area, and crystallinity of the electrode material.